The present invention relates to a method for the production of rubber mixtures with which the rubber is plasticized and/or masticated in an interior mixer (kneader) in batches and is treated with non-reactive additives; on the basis of the thus created basic mixture, the finished mixture is processed in batches by adding reactive additives.
In such a method, it is necessary to heat up the rubber in the first phase by supplying it with mechanical energy to such an extent that it becomes kneadable (plasticized) and capable of receiving the additives required for the development of its characteristic features, particularly the highly active fillers. In the second phase, the addition of the reactive additives follows.
The invention is based on the fact that the majority of rubber mixtures, particularly those for the production of pneumatic vehicle tires (for example, mixtures for tire treads, mixtures designed for adhering to steel and silica gel mixtures) contains high amounts of highly active fillers, and that it is required for the production of basic mixtures, i.e., mixtures which do not yet contain reactive additives, to carry out several mixing procedures in order to obtain kneadable basic mixtures which can be processed easily. Moreover, expensive ram kneaders are required for the production of basic mixtures, and they are usually provided with plasticizer injection pumps. For storing, transport and weighing of the fillers, the ram kneaders have to be provided with extensive additional devices, as well as with conveyance extruders for the additional processing of the basic mixtures which are often still tenacious.
Accordingly, the above-mentioned first phase of the production of the basic mixture is divided into two processing steps. In the first processing step, the rubber is heated up by kneading (plasticized or masticated), if necessary, homogeneous rubber blends are produced, respectively, natural rubber is broken down (masticated). In the second processing step, the highly active fillers, respectively, the nonreactive additives are added in the same inner mixer.
However, for all these processes, a basic mixture kneader is required which is very expensive in its initial costs, in order to be able to carry out plasticizing at relatively low rotation speeds of the rotors to prevent too high thermal stresses and non-homogeneities.
It is, therefore, an object of the present invention to suggest a method of the aforementioned kind which is comparably simpler and more economic.